It is well known that the components of most pneumatic tire constructions must be assembled in a way which promotes good tire uniformity in order to provide proper tire performance. For example, a tread which “snakes” as it goes around the tire circumference will cause wobbling as the tire is operated. For example, a carcass ply which is lopsided (longer cords on one side of the tire than the other side) can cause a variety of tire nonuniformity problems including static imbalance and radial force variations. For example, a tire which is not meridionally symmetric (e.g., tread not centered between beads) can cause a variety of tire nonuniformity problems including couple imbalance, lateral force variations, and conicity. Therefore, in order to meet typical tire performance requirements, the tire industry generally expends considerable effort in producing tires with good uniformity. Tire uniformity is generally considered to mean tire dimensions and mass distributions which are uniform and symmetric radially, laterally, circumferentially, and meridionally, thereby producing acceptable results for measurements of tire uniformity including static and dynamic balance, and also including radial force variation, lateral force variation, and tangential force variation as measured on tire uniformity machines which run the tire under load on a road wheel.
Although certain degrees of tire nonuniformity can be corrected in post-assembly manufacturing (e.g., by grinding), and/or in use (e.g., applying balance weights to the rim of a tire/wheel assembly), it is preferable (and generally more efficient) to build-in tire uniformity as much as possible. Typical tire building machines comprise a tire building drum around which the tire components are wrapped in successive layers including, for example, an innerliner, one or more carcass plies, optional sidewall stiffeners and bead area inserts (e.g., apex), sidewalls, and bead wire rings (beads). After this layering, the carcass ply ends are wrapped around the beads, the tires are blown up into a toroidal shape, and the tread/belt package is applied. Typically the tire building drum is in a fixed location on the plant floor, and the various layers of components are applied manually or automatically using tooling registered to reference points on the fixed drum in order to ensure component placement with the desired degree of precision. The tooling is generally fixed relative to the tire building drum, for example a guide wheel on an arm extending from the same frame (machine base) which supports the tire building drum.
The present invention addresses the unique problems of alignment and registration which arise when the tire building drum is no longer fixed, but instead is a work-piece in a flexible manufacturing system (FMS) wherein the build drum is moved between automated work stations for application of successive component layers in successive work stations. The context of the present invention is an FMS having work-pieces (tire building drums) which are too large to allow the use of a precision pallet conveyor, so the tire building drums are moved (propelled) by other means which are not necessarily able, by themselves, to achieve sufficient accuracy in positioning the tire building drums relative to the work stations. The work stations each have a centerline, or “working axis” of the work station tire assembly devices (tools). Thus, one problem to be addressed is to precisely align the axis of the tire building drum with the working axis in each work station. Such alignment includes assuring that each point along the entire drum length of the tire building drum axis of revolution is within a specified precision distance of the work station working axis, i.e., alignment comprises making the tire building drum axis of revolution coincident with the work station working axis. A second problem, related to the first, is to precisely register the longitudinal position of the tire building drum relative to each work station. A solution to both problems provides three dimensional positioning of the tire building drum relative to the tools and devices of each work station with the desired degree of precision.
U.S. Pat. No. 4,314,864 (Loeffler, et al; 1982) discloses a method and apparatus for building a tire wherein a tire assembly drum (11) is mounted by means of a drum support (15) on a longitudinally movable carriage (12) which moves on a guideway (20) past a plurality of operation stations (A–G) spaced longitudinally along the guideway. Under control of an operator, the carriage/drum is moved to each station in succession, first to last, for successive tire assembly operations. Mechanical datum (30), fixedly located at each operation station, are provided to engage mechanical locators (31) secured to the carriage, and a bladder (42) is provided selectively to cause engagement of the locators with the mechanical datum at each successive station to locate the tire assembly drum precisely with respect to the operation station. After operations at the last operation station, the carriage is returned to the first operation station. The carriage is attached to an operator's platform (16) with which it moves longitudinally, propelled by a drive system (22) which moves the operator's platform. The carriage is individually supported on wheels (19) that ride along individual tracks, or rails (20) that form the guideway. Similarly, wheels (21) are provided under the operator's platform which roll along the ground powered by the drive system. An operator is normally positioned on the operator's platform with ready access to power and sequencing panels and controls. The carriage wheels and rails appear similar in construction to railroad rails and flanged wheels. The platform is controlled to stop the carriage at the various operation stations and does so with relative accuracy. Precise positioning is obtained by use of mechanical locators on the carriage which, upon lowering of the carriage by means of the bladder, interfit with a mechanical datum fixed at each operation station. The mechanical datum comprises preferably at least three frustroconical dogs (30) anchored in the floor. The mechanical locators comprise orienting plates 31 secured to the frame of the carriage, each having an aperture (33) the periphery of which is conically tapered to mate with one of the frustroconical dogs. In order to permit the carriage to move independent of the platform as it comes to rest in positive alignment upon the dogs, a tapered pin (45) and bracket (53) are used to attach the carriage to the platform. The tapered pin is mounted vertically on the carriage and has a long shank of reduced diameter. The bracket is mounted on the operator's platform and has a vertical tapered bore which matingly engages a conical portion of the tapered pin such that when the carriage is lowered onto the dogs, the tapered pin lowers, moving the reduced diameter shank into the bore of the bracket, thereby allowing relative movement between the pin and bracket, and therefore between the carriage and platform. A limitation of the disclosed tire building apparatus/method is that there is only one tire assembly drum being used to assemble only one tire at a time in all the operation stations, using them in sequence and then reversing direction to return to the first station to begin the next tire. Also, precision location involves sliding of surfaces between the dogs and orienting plates, thereby inducing wear and subsequent loss of precision necessitating part replacement for maintenance.
U.S. Pat. No. 1,309,894 (Kilborn; 1919; assigned to Goodyear), discloses an early form of tire assembly automation wherein a number of carcass-mounting units (5, FIG. 1) are arranged in a linear “aligned” series, and a treading/stitching machine (12) rides on a trackway (7) for intermittent correlation with each of the carcass-supporting units of the series. Referring to FIG. 4, the trackway is seen to comprise a pair of flat-topped rails (23, 24) upon which ride wheels (22, 18) which have flanges (28, 26) to hold the wheels on the rails similar to conventional railroad rails and wheels. There are two front wheels (22) and two rear wheels (18). The treading/stitching machine can be rolled off the rails to ride on the floor by means of an extra flange (28) on the front wheels sized to allow the machine to roll about on the wheel flanges. The machine is “readily pushed into a centered position before any of the tires, its weight serving to maintain it stationary during the stitching of any of the tire treads . . . ” upon the trackway by a human operator, who uses a pointer (58, FIG. 3) to center the machine relative to a tire carcass: “The operator has but to mark the center of a tire carcass and arrange the machine with the pointer (58) in alignment with the mark on the tire.”
The present invention is intended to overcome the limitations of the prior art by providing method and apparatus for alignment of moving tire building drums in automated tire building systems.